Multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes a body and at least two outer electrodes. The body includes first and second main surfaces, an inner layer portion and first and second outer layer portions. In the inner layer portion, dielectric layers and conductive layers are alternately stacked on each other. The second outer layer portion includes an outer portion and an inner portion. A boundary region adjacent to the inner portion in the outer portion inclines toward the first main surface.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a multilayer ceramic capacitor, amultilayer ceramic capacitor series including the same, and a multilayerceramic capacitor mount body including the same.

2. Description of the Related Art

An example of the related art that discloses a multilayer ceramiccapacitor in which the occurrence of cracks may be suppressed isJapanese Unexamined Patent Application Publication No. 2012-248581. Inthe multilayer ceramic capacitor disclosed in this publication, a baseunit includes an inner electrode body (inner layer portion) and firstand second dielectric bodies (outer layer portions). The inner electrodebody is constituted by first inner electrodes and second innerelectrodes facing each other with a dielectric member therebetween andstacked on each other. The first and second dielectric bodies sandwichthe inner electrode body therebetween in the stacking direction. Thefirst dielectric body including a first main surface of the base unit isthicker than the second dielectric body including a second main surfaceof the base unit in the stacking direction.

One of the reasons why cracks occur is as follows. When a substratehaving a multilayer ceramic capacitor mounted thereon is deflected dueto an external force, an external stress is produced. This externalstress acts on a dielectric layer of the multilayer ceramic capacitor,which causes the occurrence of cracks. The present inventors havediscovered another reason why cracks occur. When a multilayer ceramiccapacitor is subjected to firing, an internal stress is produced due tothe difference in the coefficient of thermal contraction betweendielectric layers and conductive layers. This internal stress acts onthe boundary between the inner layer portion and the outer layerportion, thereby causing the occurrence of cracks (delamination).

In the multilayer ceramic capacitor disclosed in the above-describedpublication, the occurrence of cracks caused by an external stress maybe suppressed, but the occurrence of cracks caused by an internal stressproduced by the difference in the coefficient of thermal contractionbetween dielectric layers and conductive layers is not considered.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a multilayerceramic capacitor in which it is possible to significantly reduce orprevent the occurrence of cracks caused by an internal stress producedby the difference in the coefficient of thermal contraction betweendielectric layers and conductive layers.

According to a preferred embodiment of the present invention, amultilayer ceramic capacitor includes a body and two outer electrodes.The body includes a plurality of dielectric layers and a plurality ofconductive layers stacked on each other and includes first and secondmain surfaces opposing each other in a stacking direction. The two outerelectrodes are disposed on at least some surfaces of the body and areelectrically connected to at least some of the plurality of conductivelayers. The plurality of conductive layers include first conductivelayers connected to one of the two outer electrodes and secondconductive layers connected to the other one of the two outerelectrodes. The body includes first and second end surfaces which opposeeach other so as to connect the first and second main surfaces and firstand second side surfaces which oppose each other so as to connect thefirst and second main surfaces and also to connect the first and secondend surfaces. The body includes an inner layer portion and first andsecond outer layer portions which sandwich the inner layer portiontherebetween. The first and second conductive layers and at least someof the plurality of dielectric layers are stacked on each other in thestacking direction within the inner layer portion. The inner layerportion includes an area extending from a first outermost conductivelayer positioned closest to the first main surface among the pluralityof conductive layers through a second outermost conductive layerpositioned closest to the second main surface among the plurality ofconductive layers. The second outer layer portion includes an outerportion including the second main surface and an inner portion disposedbetween the outer portion and the inner layer portion. The compositionratio of Si to Ti of the dielectric layer included in the outer portionis higher than that of the dielectric layers included in the inner layerportion and the dielectric layer included in the inner portion. Theouter portion includes a boundary region adjacent to the inner portionwhich has a larger Si content compared to a central region of the outerportion. The boundary region includes a portion which inclines towardthe first main surface as the boundary region gets closer to one of theend surfaces or the side surfaces.

According to preferred embodiments of the present invention, theboundary region preferably is not a simple flat surface, but has a shapesuch that the outer portion clamps the inner portion via deformedportions. It is thus possible to significantly reduce or prevent theoccurrence of cracks caused by an internal stress produced due to thedifference in the coefficient of thermal contraction between dielectriclayers and conductive layers.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a multilayer ceramic capacitoraccording to a first preferred embodiment of the present invention.

FIGS. 2 and 3 are sectional views taken along lines II-II and III-III,respectively, of FIG. 1.

FIGS. 4 and 5 are sectional views taken along lines IV-IV and V-V,respectively, of FIG. 2.

FIGS. 6A and 6B are sectional views illustrating a modified example ofthe multilayer ceramic capacitor of the first preferred embodiment ofthe present invention.

FIG. 7 is a flowchart illustrating a manufacturing method for amultilayer ceramic capacitor according to a second preferred embodimentof the present invention.

FIG. 8 is an exploded perspective view illustrating the manufacturingmethod for a multilayer ceramic capacitor according to the secondpreferred embodiment of the present invention.

FIGS. 9 and 10 are sectional views illustrating the manufacturing methodfor a multilayer ceramic capacitor according to the second preferredembodiment of the present invention.

FIG. 11 is a sectional view illustrating a multilayer ceramic capacitormount body according to a third preferred embodiment of the presentinvention.

FIG. 12 is a plan view of a multilayer ceramic capacitor seriesaccording to a fourth preferred embodiment of the present invention.

FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12.

FIGS. 14 through 16 are sectional views illustrating a manufacturingmethod for a multilayer ceramic capacitor according to a fifth preferredembodiment of the present invention.

FIG. 17 is a schematic view illustrating a state in which a substratehaving a multilayer ceramic capacitor thereon is bent in a secondexperiment.

FIG. 18 is a sectional view illustrating an evaluation method for thenonlinearity of a boundary region in a third experiment.

FIG. 19 illustrates an example of an enlarged image of a cross sectionof a multilayer ceramic capacitor observed with a scanning electronmicroscope (SEM).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below, with reference to the accompanyingdrawings, of a multilayer ceramic capacitor, a multilayer ceramiccapacitor series including the same, and a multilayer ceramic capacitormount body including the same according to preferred embodiments of thepresent invention. In the following description of the preferredembodiments, the same element or corresponding elements shown in thedrawings are designated by like reference numeral, and an explanationthereof will be given only once. The multilayer ceramic capacitor willbe simply referred to as a “capacitor”.

First Preferred Embodiment

A capacitor 10 according to a first preferred embodiment of the presentinvention will be described below with reference to FIGS. 1 through 5.

FIG. 1 is an external perspective view of the capacitor 10. FIGS. 2 and3 are sectional views taken along lines II-II and III-III, respectively,of FIG. 1. FIGS. 4 and 5 are sectional views taken along lines IV-IV andV-V, respectively, of FIG. 2. In FIGS. 1 through 5, the length directionof a body 11, which will be discussed below, is indicated by L, thewidth direction thereof is indicated by W, and the height directionthereof is indicated by T.

The stacking direction of dielectric layers 12 and conductive layers 13is perpendicular to the length direction L and the width direction W ofthe body 11. That is, the stacking direction of the dielectric layers 12and the conductive layers 13 is parallel with the height direction T ofthe body 11.

The capacitor 10 includes the body 11 and two outer electrodes 14. Thebody 11 includes a plurality of dielectric layers 12 and a plurality ofconductive layers 13 stacked on each other, and includes first andsecond main surfaces 111 and 112 opposing each other in the stackingdirection. The two outer electrodes 14 are disposed on at least somesurfaces of the body and are electrically connected to at least some ofthe plurality of conductive layers 13. The body 11 includes first andsecond end surfaces 113 and 114, which define and function as two endsurfaces. The first and second end surfaces 113 and 114 oppose eachother so as to connect the first and second main surfaces 111 and 112.The body 11 also includes first and second side surfaces 115 and 116,which serve as two side surfaces. The first and second side surfaces 115and 116 oppose each other so as to connect the first and second mainsurfaces 111 and 112 also to connect the first and second end surfaces113 and 114.

The shortest distance between the first and second side surfaces 115 and116 is smaller than that between the first and second end surfaces 113and 114. That is, the width W₀ of the body 11 in the width direction Wis smaller than the length L₀ of the body 11 in the length direction L.The body 11 preferably has a rectangular or substantially rectangularparallelepiped shape, and may have a rounded portion at least in one ofa corner and a ridge of the body 11.

The body 11 includes an inner layer portion 11 m and first and secondouter layer portions 12 b 1 and 12 b 2 which sandwich the inner layerportion 11 m therebetween. The inner layer portion 11 m includes an areaextending from a first outermost conductive layer 13 positioned closestto the first main surface 111 to a second outermost conductive layer 13positioned closest to the second main surface 112 in the stackingdirection. In the inner layer portion 11 m, some of the plurality ofdielectric layers 12 and the plurality of conductive layers 13 arestacked on each other. The first outer layer portion 12 b 1 includes afirst dielectric layer 12 x, which is the dielectric layer positionedclosest to the first main surface 111 among the plurality of dielectriclayers 12. The second outer layer portion 12 b 2 includes an outerportion 12 b 22 and an inner portion 12 b 21. The outer portion 12 b 22includes a second dielectric layer 12 y, which is the dielectric layerpositioned closest to the second main surface 112 among the plurality ofdielectric layers 12. The inner portion 12 b 21 includes a dielectriclayer 12 x positioned between the outer portion 12 b 22 and the innerlayer portion 11 m. In the first preferred embodiment, the height h₂₁ ofthe inner portion 12 b 21 preferably is about 60 μm or smaller, forexample.

As shown in FIG. 2, as viewed from the width direction, the body 11includes end margin portions 12 e between the inner layer portion 11 mand the first and second end surfaces 113 and 114 in the lengthdirection. In the end margin portions 12 e, conductive layers 13connected to one end surface do not extend to the other end surface. Ifthe plurality of conductive layers 13 are alternately connected to thetwo end surfaces, in the end margin portion 12 e at one end surface,about half the number of conductive layers 13 extend and connect to thisend surface. The conductive layers 13 connected to the other end surfaceare not present in this end margin portion 12 e, and a dielectric memberfills portions from the positions at which such conductive layers 13 aredisconnected to the end surface. In the end margin portion 12 e at theother end surface, the remaining about half the number of conductivelayers 13 extend to the other end surface. As viewed from the widthdirection, the outer portion 12 b 22 includes a boundary region 12 zwhich is adjacent to the inner portion 12 b 21. The boundary region 12 zincludes portions boundary region in the end margin portions 12 eincline toward the first main surface 111 as the boundary region 12 zgets closer to the first and second end surfaces 113 and 114. That is,the boundary region 12 z includes deformed portions 9.

As shown in FIGS. 2 and 3, the plurality of dielectric layers 12 includea plurality of first dielectric layers 12 x and the second dielectriclayer 12 y, which are formed from ceramic green sheets made of differentcompositions, which will be discussed later.

The configuration of the first outer layer portion 12 b 1 is notrestricted to that discussed above. The first outer layer portion 12 b 1may include an outer portion including a second dielectric layer 12 ypositioned closest to the first main surface 111 and an inner portionincluding a first dielectric layer 12 x positioned between the outerportion and the inner layer portion 11 m.

In the inner layer portion 11 m, first dielectric layers 12 x, which aresome of the plurality of dielectric layers 12, and all the conductivelayers 13 are alternately stacked on each other. That is, the innerlayer portion 11 m includes all the conductive layers 13. In otherwords, if the conductive layers 13 connected to one end surface arereferred to as “first conductive layers” and the conductive layers 13connected to the other end surface are referred to as “second conductivelayers”, the inner layer portion 11 m is a portion in which the firstand second conductive layers are stacked on each other. All theconductive layers 13 preferably are rectangular or substantiallyrectangular, as viewed from above, as shown in FIGS. 4 and 5.

As shown in FIG. 2, all the conductive layers 13 may be electricallyconnected to either one of the two outer electrodes 14. In the firstpreferred embodiment, all the conductive layers 13 are electricallyconnected to one of the two outer electrodes 14. Alternatively, at leastsome of the conductive layers 13 may be electrically connected to one ofthe outer electrodes 14. That is, among the plurality of conductivelayers 13, there may be some conductive layers 13 that are notelectrically connected to any outer electrodes 14.

As shown in FIG. 2, the two outer electrodes 14 are disposed at bothends of the body 11 in the length direction L. More specifically, one ofthe two outer electrodes 14 is disposed at one end of the body 11 closeto the first end surface 113 in the length direction L, while the otherone of the two outer electrodes 14 is disposed at the other end of thebody 11 close to the second end surface 114 in the length direction L.In the first preferred embodiment, one of the two outer electrodes 14 isdisposed from the first end surface 113 continuously to the first andsecond main surfaces 111 and 112 and to the first and second sidesurfaces 115 and 116. The other one of the two outer electrodes 14 isdisposed from the second end surface 114 continuously to the first andsecond main surfaces 111 and 112 and to the first and second sidesurfaces 115 and 116. However, the arrangement of the two outerelectrodes 14 is not restricted to that described above. The two outerelectrodes 14 may be disposed on some surfaces of the body 11 so thatthey can be electrically connected to the plurality of conductive layers13 and so that the capacitor 10 can be mounted.

One of the two outer electrodes 14 is connected to some of the pluralityof conductive layers 13 on the first end surface 113, while the otherone of the two outer electrodes 14 is connected to the remainingconductive layers 13 on the second end surface 114. The conductivelayers 13 connected to the first end surface 113 and the remainingconductive layers 13 connected to the second end surface 114 arealternately stacked on each other such that they face each other with afirst dielectric layer 12 x therebetween in the inner layer portion 11m.

As shown in FIG. 3, the height T₁ of the inner layer portion 11 m in thestacking direction of the body 11 is greater than the width W₁ of theinner layer portion 11 m where the plurality of conductive layers 13 aredisposed in the width direction W of the body 11. The width direction Wis a direction in which the first and second side surfaces 115 and 116can be connected with the shortest distance. The height T₁ of the innerlayer portion 11 m may be greater than the width W₀ of the body 11 in adirection in which the first and second side surfaces 115 and 116 can beconnected with the shortest distance.

The height h₂₂ of the outer portion 12 b 22 is equal to or greater thanthe height h₂₁ of the inner portion 12 b 21. The height h₂₂ of the outerportion 12 b 22 is preferably about 30 μm or greater, for example, whichwill be discussed later. The height h₂₁ of the inner portion 12 b 21 ispreferably about 20 μm or greater, for example, which will be discussedlater.

In the first preferred embodiment, the second outer layer portion 12 b 2is thicker than the first outer layer portion 12 b 1. That is, theheight h₂ of the second outer layer portion 12 b 2 is greater than theheight h₁ of the first outer layer portion 12 b 1. The inner portion 12b 21 is thicker than the first outer layer portion 12 b 1. That is, theheight h₂₁ of the inner portion 12 b 21 is greater than the height h₁ ofthe first outer layer portion 12 b 1.

The height T₀ of the body 11 in the stacking direction of the body 11 isequal to the total height of the height T₁ of the inner layer portion 11m, the height h₁ of the first outer layer portion 12 b 1, and the heighth₂ of the second outer layer portion 12 b 2.

In the first preferred embodiment, the deformed portion 9 is preferablyprovided at each end of the boundary region 12 z in the length directionL. Accordingly, the boundary region 12 z, as a whole, is not a simpleflat surface. It is thus less likely that delamination will occurbetween the first dielectric layer 12 x and the second dielectric layer12 y. The boundary region 12 z preferably has a shape such that theouter portion 12 b 22 clamps the inner portion 12 b 21 therebetween viathe deformed portions 9. Accordingly, when the outer portion 12 b 22contracts, it compresses the inner portion 12 b 21, and as a result, theinner portion 12 b 21 compresses the inner layer portion 11 m. Thus, itis also less likely that cracks will occur at and near the corners ofthe inner layer portion 11 m close to the second main surface 112.

Modified Example

More preferably, instead of the capacitor 10, a capacitor 10 iconfigured as shown in FIG. 6A is used. That is, it is preferable that,as viewed from the width direction, the points of the boundary region 12z which reach the end surfaces 113 and 114 belong to a region where theinner layer portion 11 m is projected toward the end surfaces 113 and114. That is, as shown in FIG. 6A, the positions at which both ends ofthe boundary region 12 z are in contact with the first and second endsurfaces 113 and 114 are closer to the first main surface 111 than thesecond outermost conductive layer 13 is. In other words, in a crosssection perpendicular to a direction in which the first and second sidesurfaces 115 and 116 are connected to each other (in particular, a crosssection passing through the center of the body 11), the distance betweenthe points of the boundary region 12 z which reach the first and secondend surfaces 113 and 114 and the second main surface 112 is greater thanthe shortest distance between the inner layer portion 11 m and thesecond main surface 112. In this manner, if the deformed portions 9penetrate deeply to such a degree as to reach the side area of the innerlayer portion 11 m, the outer portion 12 b 22 reliably clamps, not onlythe inner portion 12 b 21, but also the inner layer portion 11 mtherebetween, via the deformed portions 9. It is thus even less likelythat cracks will occur at and near the corners of the inner layerportion 11 m close to the second main surface 112.

A WT cross section of the capacitor 10 i shown in FIG. 6A is representedby the one shown in FIG. 6B. It is preferable that, as viewed from thelength direction, the points of the boundary region 12 z which reach theside surfaces 115 and 116 belong to a region where the inner layerportion 11 m is projected toward the first and second side surfaces 115and 116. As shown in FIG. 6B, the positions at which both ends of theboundary region 12 z are in contact with the first and second sidesurfaces 115 and 116 are closer to the first main surface 111 than theconductive layer 13 within the inner layer portion 11 m positionedclosest to the second main surface 112 is. With this configuration, too,it is even less likely that cracks will occur at and near the corners ofthe inner layer portion 11 m close to the second main surface 112.

Referring back to FIGS. 1 to 5, a description of the configuration ofthe capacitor 10 will continue.

As shown in FIG. 3, as viewed from the length direction, the body 11includes side margin portions 12 c between the inner layer portion 11 mand the first and second side surfaces 115 and 116 in the widthdirection. In the side margin portions 12 c, the conductive layers 13 donot extend to the first and second side surfaces 115 and 116, in otherwords, the conductive layers 13 are not present, and a dielectric memberfills the side margin portions 12 c. As viewed from the lengthdirection, the outer portion 12 b 22 includes a boundary region 12 zwhich is adjacent to the inner portion 12 b 21, the boundary regionincludes portions in the side margin portions 12 c which incline towardthe first main surface 111 as the boundary region 12 z gets closer tothe first and second side surfaces 115 and 116. That is, the boundaryregion 12 z includes deformed portions 9.

Since the conductive layers 13 are not contained within the side marginportions 12 c, the density of the side margin portions 12 c is smallerthan that of the end margin portions 12 e. Accordingly, it is preferablethat the deformation amount of the deformed portions 9 of the boundaryregion 12 z in the side margin portions 12 c be greater than that of thedeformed portions 9 of the boundary region 12 z in the end marginportions 12 e.

In other words, the distance between the points of the boundary region12 z which reach the first and second side surfaces 115 and 116 and thesecond main surface 112 in a cross section passing through the center ofthe body 11 and being perpendicular to a direction in which the firstand second end surfaces 113 and 114 are connected to each other isgreater than the distance between the points of the boundary region 12 zwhich reach the first and second end surfaces 113 and 114 and the secondmain surface 112 in a cross section passing through the center of thebody 11 and being perpendicular to a direction in which the first andsecond side surfaces 115 and 116 are connected to each other. That is, amaximum distance in the stacking direction T between the second mainsurface 112 and the boundary region 12 z at a cross section of the body11 which is perpendicular to the length direction L and including acenter of the body 11 is greater than a maximum distance in the stackingdirection T between the second main surface 112 and the boundary region12 z at a cross section of the body 11 which is perpendicular to thewidth direction W and including the center of the body 11.

As shown in FIG. 2, as viewed from the width direction, a portion of thefirst outermost conductive layer 13 in the end margin portion 12 epreferably inclines toward the second main surface 112 as the firstoutermost conductive layer 13 gets closer to one of the first and secondend surface 113 and 114 which is connected to the first outermostconductive layer 13. Similarly, a portion of the second outermostconductive layer 13 in the end margin portion 12 e preferably inclinestoward the first main surface 111 as the second outermost conductivelayer 13 gets closer to one of the first and second end surface 113 and114 which is connected to the second outermost conductive layer 13. Withthis arrangement, in the first and second outermost conductive layers13, cracks (delamination) caused by the difference in the thermalcontraction are less likely to occur. Since the second outer layerportion 12 b 2 is thicker than the first outer layer portion 12 b 1, thedifference in the thermal contraction in the second outermost conductivelayer 13 is increased, and cracks are likely to occur. Accordingly, theamount by which the second outermost conductive layer 13 inclines ispreferably greater than that by which the first outermost conductivelayer 13 inclines. The amounts by which the first and second outermostconductive layers 13 incline are determined by a method similar to thatfor measuring the shortest distance d when evaluating the nonlinearityof the boundary region 12 z in third and fourth experiments, which willbe discussed later.

It is preferable that, in the width direction W of the body 11, themaximum width of the side margin portions 12 c provided between each ofthe first and second side surfaces 115 and 116 and the inner layerportion 11 m be greater than the height h₁ of the first outer layerportion 12 b 1. It is also preferable that the average width ((W₀−W₁)/2)of the side margin portions 12 c be greater than the height h₁ of thefirst outer layer portion 12 b 1. It is more preferable that the maximumwidth or the average width ((W₀−W₁)/2) of the side margin portions 12 cbe greater than about μm and smaller than about 90 μm, for example. Itis also preferable that the maximum width of the side margin portions 12c be greater than the height h₂₁ of the inner portion 12 b 21. Themaximum width and the average width ((W₀−W₁)/2) of the side marginportions 12 c will be discussed later.

It is preferable that, in the length direction L of the body 11, themaximum length of the end margin portions 12 e provided between each ofthe first and second end surfaces 113 and 114 and the inner layerportion 11 m be greater than the height h₁ of the first outer layerportion 12 b 1. It is also preferable that the average length((L₀−L₁)/2) of the end margin portions 12 e be greater than the heighth₁ of the first outer layer portion 12 b 1. It is more preferable thatthe maximum length or the average length ((L₀−L₁)/2) of the end marginportions 12 e be greater than about 30 μm and smaller than about 90 μm,for example. It is also preferable that the maximum length of the endmargin portions 12 e be greater than the height h₂₁ of the inner portion12 b 21. The maximum length and the average length ((L₀−L₁)/2) of theend margin portions 12 e will be discussed later.

Some of the components contained in the capacitor 10 will be describedin detail.

As a material for each of the plurality of conductive layers 13, ametal, such as Ni, Cu, Ag, Pd, or Au, or an alloy containing at leastone of such metals (for example, an alloy of Ag and Pd) may be used. Thethickness of each conductive layer 13 after a firing step is preferablyabout 0.3 μm to about 2.0 μm, for example.

The two outer electrodes 14 each include a foundation layer which coversboth end portions of the body 11 and a plated layer which covers thisfoundation layer. As a material for the foundation layer, a metal, suchas Ni, Cu, Ag, Pd, or Au, or an alloy containing at least one of suchmetals (for example, an alloy of Ag and Pd) may be used. The thicknessof the foundation layer is preferably about 10.0 μm to about 50.0 μm,for example.

The foundation layer may be formed by baking a conductive paste appliedto both end portions of the body 11 which has been fired. Alternatively,the foundation layer may be formed by firing, together with theconductive layers 13, a conductive paste applied to both end portions ofthe body 11 which has not been fired. Alternatively, the foundationlayer may be formed by plating both end portions of the body 11 or bycuring a resin paste containing conductive particles applied to both endportions of the body 11.

If the foundation layer is made of a resin paste containing conductiveparticles, it is possible to reduce a load imposed on the body 11 causedby an external stress which is produced when a mounting member havingthe capacitor 10 mounted thereon is deflected due to an external forceand thus to significantly reduce or prevent the occurrence of cracks inthe body 11. Accordingly, by forming the second outer layer portion 12 b2 thick and then by forming the two outer electrodes 14 having a resinlayer containing conductive particles, the occurrence of cracks in thebody 11 is further significantly reduced or prevented.

As a material for the plated layer, a metal, such as Sn, Ni, Cu, Ag, Pd,or Au, or an alloy containing at least one of such metals (for example,an alloy of Ag and Pd) may be used.

The plated layer may be constituted by a plurality of layers. In thiscase, the plated layer is preferably a two-layer structure in which a Snplated layer is formed on a Ni plated layer. In this case, the Ni platedlayer defines and functions as a solder barrier layer, while the Snplated layer improves solder wettability. The thickness of one platedlayer is preferably about 1.0 μm to about 10.0 μm, for example.

The dielectric layers 12 each contain a perovskite compound expressed byABO₃ (“A” contains Ba, and “B” contains Ti, and O is oxygen) as aprincipal component. That is, the plurality of first dielectric layers12 x and the second dielectric layer 12 y each contain barium titanate(BaTiO₃) as a principal component.

The plurality of dielectric layers 12 each contain Si as a secondarycomponent. Si is contained in the dielectric layers 12 by adding a Sicompound, such as glass or SiO₂, as a secondary component to aperovskite compound expressed by ABO₃ as a principal component. Anothercompound, such as a Mn compound, an Mg compound, a Co compound, a Nicompound, or a rare earth compound, may be added to a perovskitecompound expressed by ABO₃.

The composition ratio of Si to Ti of the second dielectric layer 12 ydefining the outer portion 12 b 22 is higher than that of the firstdielectric layers 12 x included in the inner layer portion 11 m, thefirst dielectric layer 12 x defining the first outer layer portion 12 b1, and the first dielectric layer 12 x defining the inner portion 12 b21. The composition ratio of Si and other components to Ti may berepresented by a molar ratio. The molar ratio of Si to Ti of each of thedielectric layers 12 may be measured by using a wavelength-dispersiveX-ray spectrometer (WDX).

The molar ratio of Si to Ti of the second dielectric layer 12 y definingthe outer portion 12 b 22 is preferably about 1.3 to 3.0 mol percent(%), for example. If the molar ratio of Si to Ti of the seconddielectric layer 12 y is lower than about 1.3 mol % or higher than about3.0 mol %, the reliability of the outer portion 12 b 22 may be impaired.

The molar ratio of Si to Ti of the second dielectric layer 12 y definingthe outer portion 12 b 22 is preferably higher than that of the firstdielectric layer 12 x forming the inner portion 12 b 21 by about 0.4 mol% or higher, and more preferably, by about 0.8 mol % or higher, forexample.

A portion near the boundary region 12 z adjacent to the inner portion 12b 21 in the outer portion 12 b 22 has a higher content of Si than acentral region 12 m of the outer portion 12 b 22. A surface layersection 12 s of the outer portion 12 b 22 close to the second mainsurface 112 also has a higher content of Si than the central region 12 mof the outer portion 12 b 22. The boundary region 12 z and the surfacelayer section 12 s of the outer portion 12 b 22 having a high contentratio of Si may be identified by element mapping created by using afield emission wavelength-dispersive X-ray spectrometer (FE-WDX).

Second Preferred Embodiment

A manufacturing method for a capacitor according to a second preferredembodiment of the present invention will be described below withreference to FIGS. 7 through 10. The manufacturing method of the secondpreferred embodiment is a method for manufacturing the capacitor 10discussed in the first preferred embodiment.

FIG. 7 is a flowchart illustrating a manufacturing method for thecapacitor 10 in the second preferred embodiment. In this manufacturingmethod, a plurality of capacitors 10 are mass-produced at one timetogether in the following manner. Elements which will form a pluralityof capacitors 10 are processed together until a halfway point through amanufacturing process so as to fabricate a mother body. Then, the motherbody is divided into individual flexible bodies. The individual flexiblebodies are then processed, thus manufacturing a plurality of capacitors10.

The manufacturing method will be discussed below more specifically withreference to FIG. 7. In step S11, first ceramic slurry is preparedfirst. More specifically, a ceramic powder, a binder, and a solvent aremixed at a predetermined mixing ratio so as to form the first ceramicslurry.

Then, in step S12, first ceramic green sheets are formed. Morespecifically, the first ceramic slurry is formed into a sheet shape on acarrier film by using a die coater, a gravure coater, or a micro gravurecoater, thus defining the first ceramic green sheets.

Then, in step S13, mother sheets are formed. More specifically, aconductive paste is printed on each first ceramic green sheet by usingscreen printing or gravure printing such that a predetermined conductivepattern is formed on the first ceramic green sheet. As a result, amother sheet, which is a first ceramic green sheet having apredetermined conductive pattern thereon, is formed.

Mother sheets formed in step S13 will be discussed below in details.FIG. 8 is an exploded perspective view illustrating the multilayerstructure of a set of unit sheets, which will define a partial body 11 pof the capacitor 10 of the first preferred embodiment without the outerportion 12 b 22.

As shown in FIG. 8, the partial body 11 p includes a set of a pluralityof unit sheets 120 a, 130 a, and 130 b which are configured differently.More specifically, the plurality of unit sheets 120 a, 130 a, and 130 bare stacked on each other in a predetermined order and are thenpressure-bonded and fired so as to fabricate the partial body 11 p.

Each unit sheet 120 a preferably is constituted only by a ceramic basemember 12 xr on which no conductive pattern is formed. The unit sheet120 a defines a first dielectric layer 12 x of the first outer layerportion 12 b 1 or the inner portion 12 b 21 after the firing step isperformed.

The unit sheets 130 a and 130 b are each constituted by a ceramic basemember 12 xr on which a conductive pattern 13 r having a predeterminedshape is formed. The conductive patterns 13 r of the unit sheets 130 aand 130 b define the conductive layers 13 within the inner layer portion11 m after the firing step is performed. The ceramic base members 12 xrof the unit sheets 130 a and 130 b define the first dielectric layers 12x within the inner layer portion 11 m after the firing step isperformed.

The layout of the mother sheet is as follows. By using each of the unitsheets 130 a and 130 b shown in FIG. 8 as a unit, a plurality of unitsheets having the same configuration as that of the unit sheet 130 a or130 b are two-dimensionally arranged in a matrix.

Since the unit sheets 130 a and 130 b have the same configuration, unitsheets having the same conductive pattern may be used as a mother sheet.In a step of stacking a set of mother sheets, which will be discussedlater, mother sheets having the same conductive pattern are displacedfrom each other by a half pitch, thus obtaining the multilayer structureof the unit sheets 130 a and 130 b shown in FIG. 8.

As mother sheets, not only mother sheets having the conductive pattern13 r, but also first ceramic green sheets which are formed without beingsubjected to step S13 are also prepared.

Then, referring back to FIG. 7, in step S14, the mother sheets arestacked. More specifically, by stacking the plurality of mother sheetsaccording to a predetermined rule, the above-described units arepositioned within a set of the stacked mother sheets so that themultilayer structure shown in FIG. 8 is obtained.

Then, in step S15, the set of stacked mother sheets is pressure-bonded.FIG. 9 is a sectional view illustrating a state in which the set ofmother sheets are being pressure-bonded. In FIG. 9, the set of mothersheets corresponding to only one partial body 11 p is shown. In thesecond preferred embodiment, as shown in FIG. 9, a plurality of mothersheets defining the first outer layer portion 12 b 1, a plurality ofmother sheets defining the inner layer portion 11 m, and a plurality ofmother sheets defining the inner portion 12 b 21 are stacked on eachother in this order so as to define the set of mother sheets.

A flat die 91 is pressed against the mother sheets defining the innerportion 12 b 21 along the stacking direction, as indicated by an arrow92 in FIG. 9, thus pressure-bonding the set of mother sheets placed on abase 90.

In step S21, second ceramic slurry is prepared. More specifically, aceramic powder, a binder, and a solvent are mixed at a predeterminedmixing ratio so as to form the second ceramic slurry. The amount of Sicontained in the second ceramic slurry is greater than that in the firstceramic slurry.

Then, in step S22, second ceramic green sheets are formed. Morespecifically, the second ceramic slurry is formed into a sheet shape ona carrier film by using a die coater, a gravure coater, or a microgravure coater, thus defining a plurality of second ceramic greensheets.

Then, in step S23, the plurality of second ceramic green sheets arestacked on the set of mother sheets pressure-bonded in step S15. Morespecifically, the plurality of second ceramic green sheets uniquely madeof a ceramic base member 12 yr defining the second dielectric layer 12 yof the outer portion 12 b 22 are stacked on the mother sheets definingthe inner portion 12 b 21. Instead of stacking the plurality of secondceramic green sheets uniquely made of a ceramic base member 12 yr, apaste containing the second ceramic slurry may be applied onto themother sheets defining the inner portion 12 b 21.

Then, in step S24, the set of mother sheets pressure-bonded in step S15and the plurality of second ceramic green sheets are pressure-bonded.FIG. 10 is a sectional view illustrating a state in which the set ofmother sheets and the plurality of second ceramic green sheets are beingpressure-bonded. In FIG. 10, the set of mother sheets and the pluralityof second ceramic green sheets corresponding to only one flexible body11 q are shown. In FIG. 10, a flat die 91 is pressed against the mothersheets defining the outer portion 12 b 22 along the stacking directionof the set of mother sheets, as indicated by an arrow 92, thuspressure-bonding the set of mother sheets and the plurality of secondceramic green sheets. As a result, a mother body is fabricated. At thisstage, deformed portions 9 are formed at both ends of the boundaryregion 12 z.

Then, in step S25, the mother body is divided. More specifically, themother body is press-cut or cut with a dicing machine in a matrix intothe flexible bodies 11 q.

Then, in step S26, the flexible bodies 11 q are fired. Morespecifically, the flexible bodies 11 q are heated to a predeterminedtemperature so as to fire the ceramic dielectric material and theconductive material. The firing temperature is set suitably inaccordance with the type of ceramic dielectric material and the type ofconductive material, and may be set within a range of about 900° C. toabout 1300° C., for example.

Then, in step S27, the flexible bodies 11 q are barrel-polished. Morespecifically, the flexible bodies 11 q subjected to firing are sealedwithin a small box called a barrel, together with media balls having ahigher hardness than the ceramic material. Then, by rotating the barrel,the flexible bodies 11 q are polished. By performing thisbarrel-polishing, the outer surfaces (in particular, corners and ridges)of the flexible bodies 11 q are curved and rounded. As a result, thebody 11 is formed.

Then, in step S28, outer electrodes are formed. More specifically, aconductive paste is applied to an end portion including the first endsurface 113 and an end portion including the second end surface 114 ofthe body 11 so as to form a metal film, and then, the metal film isfired. Then, the metal film is sequentially Ni-plated and Sn-plated. Asa result, the two outer electrodes 14 are formed on the outer surfacesof the body 11.

In the second preferred embodiment, through the above-described seriesof steps, the capacitor 10 configured as shown in FIGS. 1 through 5 ismanufactured.

In the capacitor 10 discussed in the first and second preferredembodiments, each of the plurality of dielectric layers preferablycontains barium titanate as a principal component and Si as a secondarycomponent. The molar ratio of Si to Ti of the dielectric layer 12defining the outer portion 12 b 22 is preferably higher than that of thedielectric layers 12 included in the inner layer portion 11 m and thedielectric layer 12 defining the inner portion 12 b 21. It is preferablethat the boundary region in the outer portion 12 b 22 have a highercontent of Si than the central region 12 m of the outer portion 12 b 22since Si moves from the outer portion 12 b 22 or the inner portion 12 b21 to this boundary region.

The two outer electrodes 14 are preferably disposed on at least aportion of the second main surface 112 of the body 11. The surface layersection 12 s of the outer portion 12 b 22 close to the second mainsurface 112 preferably has a higher content of Si than the centralregion 12 m of the outer portion 12 b 22.

The composition ratio of a rare earth element to Ti of the dielectriclayers included in the inner layer portion 11 m is preferably higherthan that of the dielectric layer forming the outer portion 12 b 22.

The composition ratio of Mn to Ti of the dielectric layers included inthe inner layer portion 11 m, the dielectric layer defining the firstouter layer portion 12 b 1, and the dielectric layer defining the innerportion 12 b 21 is preferably higher than that of the dielectric layerdefining the outer portion 12 b 22.

In the capacitor 10, the molar ratio of Si to Ti of the seconddielectric layer 12 y defining the outer portion 12 b 22 is higher thanthat of the first dielectric layers 12 x included in the inner layerportion 11 m and the first dielectric layer 12 x defining the innerportion 12 b 21. That is, the outer portion 12 b 22 has a higher contentof Si than the inner portion 12 b 21. In a firing step, the coefficientof thermal contraction of a dielectric layer having a higher content ofSi is higher. Accordingly, in the firing step, the coefficient ofthermal contraction of the outer portion 12 b 22 is higher than that ofthe inner portion 12 b 21. Thus, the coefficient of thermal contractionof the outer portion 12 b 22 is closer to that of the conductive layers13 of the inner layer portion 11 m.

In the capacitor 10, it is possible to reduce an internal stress whichis produced in the firing step due to the difference in the coefficientof thermal contraction between the dielectric layers and the conductivelayers and which acts on the boundary between the inner layer portion 11m and the second outer layer portion 12 b 2. Thus, the occurrence ofcracks (delamination) at the boundary between the inner layer portion 11m and the second outer layer portion 12 b 2 is significantly reduced orprevented.

The molar ratio of Si to Ti of the second dielectric layer 12 y definingthe outer portion 12 b 22 is higher than that of the first dielectriclayer 12 x defining the inner portion 12 b 21 by about 0.4 mol % orhigher, for example. With this configuration, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe second outer layer portion 12 b 2 is effectively significantlyreduced or prevented. The molar ratio of Si to Ti of the outer portion12 b 22 is higher than that of the inner portion 12 b 21 by about 0.8mol % or higher, for example. With this configuration, the occurrence ofcracks at the boundary between the inner layer portion 11 m and thesecond outer layer portion 12 b 2 is significantly reduced or preventedeven more effectively.

As described above, the height of the outer portion 12 b 22 is equal toor greater than that of the inner portion 12 b 21. With thisconfiguration, the stress relaxing effect exhibited by the thermalcontraction of the outer portion 12 b 22 is more likely to be producedat the boundary between the inner layer portion 11 m and the secondouter layer portion 12 b 2.

The height h₂₂ of the outer portion 12 b 22 preferably is about 30 μm orgreater, for example. With this configuration, it is possible to securea sufficient contraction force which acts on the inner portion 12 b 21by the thermal contraction of the outer portion 12 b 22.

The height h₂₁ of the inner portion 12 b 21 preferably is about 20 μm orgreater, for example. With this configuration, the diffusion of Sicontained in the outer portion 12 b 22 into the inner layer portion 11 mis significantly reduced or prevented. If the content ratio of Si in theinner layer portion 11 m becomes too high, the grain growth of ceramicparticles in the first dielectric layers 12 x included in the innerlayer portion 11 m accelerates excessively in the firing step, thusreducing the withstand voltage characteristics of the first dielectriclayers 12 x. As a result, the inner layer portion 11 m is more likely tobe short-circuited. However, by setting the height h₂₁ of the innerportion 12 b 21 to be about 20 μm or greater, for example, the withstandvoltage characteristics of the first dielectric layers 12 x included inthe inner layer portion 11 m can be maintained, and thus, the occurrenceof short-circuiting of the inner layer portion 11 m is significantlyreduced or prevented.

As described above, the height h₂₁ of the inner portion 12 b 21 isgreater than the height h₁ of the first outer layer portion 12 b 1. Theadhesion force between the outer portion 12 b 22 and the inner portion12 b 21 is increased because of the configuration of the boundarytherebetween, which will be discussed later. Accordingly, even if theinner portion 12 b 21 is made to be thick to a certain degree, theoccurrence of cracks (delamination) at the boundary between the outerportion 12 b 22 and the inner portion 12 b 21 is significantly reducedor prevented. Thus, a contraction force generated by the thermalcontraction of the outer portion 12 b 22 acts on the inner portion 12 b21. It is therefore possible to reduce an internal stress which isproduced during the firing step due to the difference in the coefficientof thermal contraction between the dielectric layers and the conductivelayers and which acts on the boundary between the inner layer portion 11m and the inner portion 12 b 21. Thus, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe second outer layer portion 12 b 2 is significantly reduced orprevented.

As described above, the maximum width of the side margin portions 12 cis preferably greater than the height h₁ of the first outer layerportion 12 b 1. If the first outer layer portion 12 b 1 is thin, it ispossible to reduce an internal stress which is produced during thefiring step due to the difference in the coefficient of thermalcontraction between the dielectric layers and the conductive layers andwhich acts on the boundary between the inner layer portion 11 m and thefirst outer layer portion 12 b 1. Thus, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe first outer layer portion 12 b 1 is significantly reduced orprevented.

If the maximum width of the side margin portions 12 c is set to belarge, when pressure-bonding a set of mother sheets, the pressure ismore likely to be applied to the plurality of first dielectric layers 12x positioned in the side margin portions 12 c, thus enhancing theadherence of the first dielectric layers 12 x in the side marginportions 12 c. As a result, it is possible to significantly reduce orprevent the occurrence of cracks (delamination) in the first dielectriclayers 12 x positioned in the side margin portions 12 c.

As described above, the average width ((W₀−W₁)/2) of the side marginportions 12 c is preferably greater than the height h₁ of the firstouter layer portion 12 b 1. The half of the total width of the twoadjacent side margin portions 12 c of two adjacent bodies 11 dividedfrom the mother body corresponds to the average width ((W₀−W₁)/2).Accordingly, if the average width ((W₀−W₁)/2) of the side marginportions 12 c is set to be greater than the height h₁ of the first outerlayer portion 12 b 1, when pressure-bonding a set of mother sheets, thepressure is more likely to be applied to the plurality of firstdielectric layers 12 x positioned in the side margin portions 12 c, thusenhancing the adherence of the first dielectric layers 12 x positionedin the side margin portions 12 c. As a result, it is possible tosignificantly reduce or prevent the occurrence of cracks (delamination)in the first dielectric layers 12 x positioned in the side marginportions 12 c. That is, even if there is a difference between the widthof the side margin portion 12 c close to the first side surface 115 andthat close to the second side surface 116, both of the effect ofsignificantly reducing or preventing the occurrence of cracks(delamination) and the effect of significantly reducing or preventingthe occurrence of short-circuiting in the inner layer portion 11 m arereliably achieved.

As described above, the maximum width of the side margin portions 12 cis preferably greater than the height h₂₁ of the inner portion 12 b 21.If the inner portion 12 b 21 is thin, a contraction force exhibited bythe thermal contraction of the outer portion 12 b 22 is likely to act onthe inner portion 12 b 21. It is thus possible to effectively reduce aninternal stress which is produced during the firing step due to thedifference in the coefficient of thermal contraction between thedielectric layers and the conductive layers and which acts on theboundary between the inner layer portion 11 m and the inner portion 12 b21. As a result, the occurrence of cracks (delamination) at the boundarybetween the inner layer portion 11 m and the second outer layer portion12 b 2 is significantly reduced or prevented.

As described above, the maximum width or the average width ((W₀−W₁)/2)of the side margin portions 12 c is more preferably greater than about30 μm and smaller than about 90 μm, for example. If the maximum width orthe average width ((W₀−W₁)/2) of the side margin portions 12 c isgreater than about 30 μm, for example, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe inner portion 12 b 21 is reliably significantly reduced orprevented. If the maximum width or the average width ((W₀−W₁)/2) of theside margin portions 12 c is equal to or greater than about 90 μm, theelectrostatic capacitance of the capacitor 10 becomes too small. Thatis, by setting the maximum width or the average width ((W₀−W₁)/2) of theside margin portions 12 c to be smaller than about 90 μm, for example, asufficient electrostatic capacitance of the capacitor 10 can be secured.

As described above, the height T₁ of the inner layer portion 11 m in thestacking direction of the body 11 is greater than the width W₁ of theinner layer portion 11 m where the plurality of conductive layers 13 arepositioned in the width direction W of the body 11. The height T₁ of theinner layer portion 11 m may be greater than the width W₀ of the body11.

The adhesion force between the outer portion 12 b 22 and the innerportion 12 b 21 is increased because of the configuration of theboundary therebetween, which will be discussed later. Accordingly, evenif the adherence between the first dielectric layers 12 x positioned inthe side margin portions 12 c is decreased due to a large height of theinner layer portion 11 m, the occurrence of cracks (delamination) at theboundary between the outer portion 12 b 22 and the inner portion 12 b 21is significantly reduced or prevented. Thus, a contraction forcegenerated by the thermal contraction of the outer portion 12 b 22 actson the inner portion 12 b 21. It is therefore possible to reduce aninternal stress which is produced during the firing step due to thedifference in the coefficient of thermal contraction between thedielectric layers and the conductive layers and which acts on theboundary between the inner layer portion 11 m and the inner portion 12 b21. As a result, the occurrence of cracks (delamination) at the boundarybetween the inner layer portion 11 m and the inner portion 12 b 21 issignificantly reduced or prevented.

As described above, the maximum length of the end margin portions 12 ein the length direction L is preferably greater than the height h₁ ofthe first outer layer portion 12 b 1. If the first outer layer portion12 b 1 is thin, it is possible to reduce an internal stress which isproduced during the firing step due to the difference in the coefficientof thermal contraction between the dielectric layers and the conductivelayers and which acts on the boundary between the inner layer portion 11m and the first outer layer portion 12 b 1. Thus, the occurrence ofcracks (delamination) at the boundary between the inner layer portion 11m and the first outer layer portion 12 b 1 is significantly reduced orprevented.

If the maximum length of the end margin portions 12 e is set to belarge, when pressure-bonding a set of mother sheets, the pressure ismore likely to be applied to the plurality of first dielectric layers 12x positioned in the end margin portions 12 e, thus enhancing theadherence of the first dielectric layers 12 x in the end margin portions12 e. As a result, it is possible to significantly reduce or prevent theoccurrence of cracks (delamination) in the first dielectric layers 12 xpositioned in the end margin portions 12 e.

As described above, the average length ((L₀−L₁)/2) of the end marginportions 12 e is preferably greater than the height h₁ of the firstouter layer portion 12 b 1. The half of the total length of the twoadjacent end margin portions 12 e of two adjacent bodies 11 divided fromthe mother body corresponds to the average length ((L₀−L₁)/2).Accordingly, if the average length ((L₀−L₁)/2) of the end marginportions 12 e is set to be greater than the height h₁ of the first outerlayer portion 12 b 1, when pressure-bonding a set of mother sheets, thepressure is more likely to be applied to the plurality of firstdielectric layers 12 x positioned in the end margin portions 12 e, thusenhancing the adherence of the first dielectric layers 12 x in the endmargin portions 12 e. As a result, it is possible to significantlyreduce or prevent the occurrence of cracks (delamination) in the firstdielectric layers 12 x positioned in the end margin portions 12 e. Thatis, even if there is a difference between the length of the end marginportion 12 e close to the first end surface 113 and that close to thesecond end surface 114, both of the effect of significantly reducing orpreventing the occurrence of cracks (delamination) and the effect ofsignificantly reducing or preventing the occurrence of short-circuitingin the inner layer portion 11 m are reliably achieved.

As described above, the maximum length of the end margin portions 12 eis preferably greater than the height h₂₁ of the inner portion 12 b 21.If the inner portion 12 b 21 is thin, a contraction force exhibited bythe thermal contraction of the outer portion 12 b 22 is likely to act onthe inner portion 12 b 21. It is thus possible to effectively reduce aninternal stress which is produced during the firing step due to thedifference in the coefficient of thermal contraction between thedielectric layers and the conductive layers and which acts on theboundary between the inner layer portion 11 m and the inner portion 12 b21. As a result, the occurrence of cracks (delamination) at the boundarybetween the inner layer portion 11 m and the second outer layer portion12 b 2 is significantly reduced or prevented.

As described above, the maximum length or the average length ((L₀−L₁)/2)of the end margin portions 12 e is more preferably greater than about 30μm and smaller than about 90 μm, for example. If the maximum length orthe average length ((L₀−L₁)/2) of the end margin portions 12 e isgreater than about 30 μm, for example, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe inner portion 12 b 21 can be stably significantly reduced orprevented. If the maximum length or the average length ((L₀−L₁)/2) ofthe end margin portions 12 e is equal to or greater than about 90 μm,the electrostatic capacitance of the capacitor 10 becomes too small.That is, by setting the maximum length or the average length ((L₀−L₁)/2)of the end margin portions 12 e to be smaller than about 90 μm, forexample, a sufficient electrostatic capacitance of the capacitor 10 issecured.

As described above, the height T₁ of the inner layer portion 11 m in thestacking direction of the body 11 is greater than the length L₁ of theinner layer portion 11 m where the plurality of conductive layers 13 arepositioned in the length direction L of the body 11. The height T₁ ofthe inner layer portion 11 m may be greater than the length L₀ of thebody 11.

The adhesion force between the outer portion 12 b 22 and the innerportion 12 b 21 is increased because of the configuration of theboundary therebetween, which will be discussed later. Accordingly, evenif the adherence between the first dielectric layers 12 x positioned inthe end margin portions 12 e is decreased due to a large height of theinner layer portion 11 m, the occurrence of cracks (delamination) at theboundary between the outer portion 12 b 22 and the inner portion 12 b 21is significantly reduced or prevented. Thus, a contraction forcegenerated by the thermal contraction of the outer portion 12 b 22 actson the inner portion 12 b 21. It is therefore possible to reduce aninternal stress which is produced during the firing step due to thedifference in the coefficient of thermal contraction between thedielectric layers and the conductive layers and which acts on theboundary between the inner layer portion 11 m and the inner portion 12 b21. As a result, the occurrence of cracks (delamination) at the boundarybetween the inner layer portion 11 m and the inner portion 12 b 21 issignificantly reduced or prevented.

As described above, since each of the plurality of first dielectriclayers 12 x and the second dielectric layer 12 y contains bariumtitanate as a principal component, chemical bonding at the interfacebetween the inner portion 12 b 21 and the outer portion 12 b 22 isstrengthened, thus enhancing the adherence therebetween. As a result, itis possible to significantly reduce or prevent the occurrence of cracks(delamination) at the boundary between the inner portion 12 b 21 and theouter portion 12 b 22.

As described above, the boundary region in the outer portion 12 b 22 hasa higher content of Si than the central region 12 m of the outer portion12 b 22. The surface layer section 12 s of the outer portion 12 b 22close to the second main surface 112 also has a higher content of Sithan the central region 12 m of the outer portion 12 b 22.

A description will be given below of how to set the content ratio of Siof the boundary region in the outer portion 12 b 22 and the surfacelayer section 12 s of the outer portion 12 b 22 to be higher than thatof the central region 12 m of the outer portion 12 b 22. The firing stepfor the capacitor 10 is performed at a temperature and in a gaseousatmosphere in which Si segregates from grain boundaries of ceramicparticles. Then, in the outer portion 12 b 22 containing a greateramount of Si, the grain growth of ceramic particles is encouraged, andSi segregates from the grain boundaries of coarsened ceramic particles.Segregated Si moves along the grain boundaries of the ceramic particlesand concentrates toward the boundary in the outer portion 12 b 22 andthe surface layer section 12 s of the outer portion 12 b 22. As aresult, the content ratio of Si of the boundary region and that of thesurface layer section 12 s of the outer portion 12 b 22 become higherthan that of the central region 12 m of the outer portion 12 b 22.

The content ratio of Si of the boundary region in the outer portion 12 b22 is higher than that of the central region 12 m of the outer portion12 b 22, thus improving the adhesion force between the outer portion 12b 22 and the inner portion 12 b 21. The reason for this may be asfollows. Si which has moved along the grain boundaries of the ceramicparticles as described above fills many small gaps at the interfacebetween the outer portion 12 b 22 and the inner portion 12 b 21 so as tobond them each other. Accordingly, by separately forming the outerportion 12 b 22 and the inner portion 12 b 21, small gaps are created atthe interface between the outer portion 12 b 22 and the inner portion 12b 21. This encourages the concentration of segregated Si in the boundaryregion, thus improving the adhesion force between the outer portion 12 b22 and the inner portion 12 b 21.

The content ratio of Si of the surface layer section 12 s of the outerportion 12 b 22 close to the second main surface 112 is higher than thatof the central region 12 m of the outer portion 12 b 22, thussignificantly reducing or preventing a decrease in the mechanicalstrength of the body 11 when forming the outer electrodes 14. The reasonfor this is as follows. In the formation of the outer electrodes 14, ifglass components contained in the outer electrodes 14 react with theceramic dielectric material of the body 11, the mechanical strength ofthe body 11 is decreased. In this case, if an external force is appliedto the capacitor 10 while the capacitor 10 is being mounted or after ithas been mounted, cracks are likely to occur in the body 11 startingfrom the end of the contact area with the outer electrode 14 close tothe center of the body 11. However, if the content ratio of Si of theouter portion 12 b 22 is high, the reaction of glass componentscontained in the outer electrodes 14 with the ceramic dielectricmaterial of the body 11 is significantly reduced or prevented. As aresult, it is possible to significantly reduce or prevent a decrease inthe mechanical strength of the body 11 when forming the outer electrodes14.

In each of the plurality of dielectric layers 12, if a rare earthcompound is contained in a perovskite compound expressed by ABO₃, whichis a principal component, the molar ratio of a rare earth element to Tiof the first dielectric layers 12 x included in the inner layer portion11 m and the first dielectric layer 12 x defining the inner portion 12 b21 is preferably higher than that of the second dielectric layer 12 yforming the outer portion 12 b 22. That is, the inner layer portion 11 mand the inner portion 12 b 21 preferably contain a greater amount ofrare earth element than the outer portion 12 b 22.

As a rare earth element, Dy, Gd, Y, or La may be added to improve thefunctions of the capacitor 10. More specifically, by adding a rare earthelement, it is possible to stabilize the capacitance temperaturecharacteristics and to prolong the life of the capacitor 10 bymaintaining the insulation resistance (IR) value even under ahigh-temperature load.

A rare earth element is likely to concentrate in a grain boundary ofceramic particles or a segregation layer and also to elute towater-soluble flux. Accordingly, ceramic components containing a rareearth element may elute to an organic acid, such as adipic acid,contained in water-soluble flux used for soldering when mounting thecapacitor 10. In this case, cracks may occur in the outer layer portion12 b 2 of the body 11 which is embrittled as a result of the eluting ofceramic components.

Accordingly, the molar ratio of a rare earth element to Ti of the firstdielectric layers 12 x included in the inner layer portion 11 m and thefirst dielectric layer 12 x forming the inner portion 12 b 21 ispreferably about 0.3 mol % or higher, and the molar ratio of a rareearth element to Ti of the second dielectric layer 12 y forming theouter portion 12 b 22 is preferably lower than about 0.3 mol %, forexample.

By setting the molar ratio of a rare earth element to Ti of the firstdielectric layers 12 x included in the inner layer portion 11 m to beabout 0.3 mol % or higher, for example, it is possible to stabilize thecapacitance temperature characteristics and to prolong the life of thecapacitor 10 by maintaining the insulation resistance (IR) value evenunder a high-temperature load.

By setting the molar ratio of a rare earth element to Ti of the seconddielectric layer 12 y forming the outer portion 12 b 22 to be lower thanabout 0.3 mol %, for example, it is possible to significantly reduce orprevent the occurrence of cracks in the outer portion 12 b 22 caused bythe embrittlement of the outer portion 12 b 22 as a result of theeluting of ceramic components from the outer portion 12 b 22. Thesefeatures and advantages have been validated, as a result of conductingexperiments by changing the content of Dy used as a rare earth element.Advantages obtained by the use of Gd, Y, or La instead of Dy have alsobeen validated.

In each of the plurality of dielectric layers 12, if a Mn compound iscontained in a perovskite compound expressed by ABO₃, which is aprincipal component, the molar ratio of a Mn compound to Ti of the firstdielectric layers 12 x included in the inner layer portion 11 m, thefirst dielectric layer 12 x defining the first outer layer portion 12 b1, and the first dielectric layer 12 x defining the inner portion 12 b21 is preferably higher than that of the second dielectric layer 12 yforming the outer portion 12 b 22. That is, the inner layer portion 11 mand the inner portion 12 b 21 preferably contain a greater amount of Mnthan the outer portion 12 b 22.

The color of a ceramic dielectric layer containing a smaller amount ofMn is brighter than that containing a greater amount of Mn. Accordingly,the color of the outer portion 12 b 22 is brighter than that of theinner layer portion 11 m, the first outer layer portion 12 b 1, and theinner portion 12 b 21, which contain a greater amount of Mn. It is thuseasy to visually distinguish the first and second main surfaces 111 and112 of the capacitor 10 from each other.

When observing the capacitor 10 with an imaging camera, the orientationsof the first and second main surfaces 111 and 112 of the capacitor 10can be identified. Thus, when mounting the capacitor 10, the orientationof the capacitor 10 can be automatically set so that the second mainsurface 112 will be a mounting surface.

For example, the molar ratio of Mn to Ti of the first dielectric layers12 x included in the inner layer portion 11 m, the first dielectriclayer 12 x defining the first outer layer portion 12 b 1, and the firstdielectric layer 12 x defining the inner portion 12 b 21 is preferablyabout 0.08 mol % or higher, and the molar ratio of Mn to Ti of thesecond dielectric layer 12 y forming the outer portion 12 b 22 ispreferably lower than about 0.08 mol %, for example. These features andadvantages have been validated as a result of conducting experiments bychanging the content of Mn.

Third Preferred Embodiment

A capacitor mount body according to a third preferred embodiment of thepresent invention will be described below with reference to FIG. 11.

FIG. 11 is a sectional view illustrating a capacitor mount body 10 x ofthe third preferred embodiment. The capacitor mount body 10 x includesthe capacitor 10 and a mounting member 1 used to mount the capacitor 10thereon. The capacitor 10 is mounted on the mounting member 1 such thatthe second main surface 112 faces the mounting member 1. The mountingmember 1 may be a circuit board, for example.

The configuration of the capacitor mount body 10 x will be discussedmore specifically. A pair of lands 20 is disposed on the surface of themounting member 1 such that the lands 20 are spaced apart from eachother. The two outer electrodes 14 of the capacitor 10 and the two lands20 are electrically connected to each other by solder 30, which is abonding medium. The bonding medium is not restricted to solder, and anybonding material may be used as long as it is able to mechanically andelectrically connect the two outer electrodes 14 and the two lands 20.In FIG. 11, the two lands 20 are disposed side by side in a directionperpendicular to the plane of the drawing. In FIG. 11, only one land 20at the near side is shown, and the land 20 at the far side is hidden bythe land 20 at the near side.

A width W_(L) of the two lands 20 is smaller than the width W₀ of thebody 11. With this configuration, the two outer electrodes 14 aresubjected to a compressive stress applied from the solder 30 in thewidth direction W of the body 11. This compressive stress further actson the inner portion 12 b 21 via the outer portion 12 b 22. Accordingly,the internal stress acting on the boundary between the inner layerportion 11 m and the second outer layer portion 12 b 2 is relaxed, thussignificantly reducing or preventing the occurrence of cracks(delamination) at this boundary.

The width W_(L) of the two lands 20 is preferably smaller than the widthW₁ of the inner layer portion 11 m. In this case, the compressive stressacting on the inner portion 12 b 21 via the outer portion 12 b 22 isincreased. Accordingly, the internal stress acting on the boundarybetween the inner layer portion 11 m and the second outer layer portion12 b 2 is further relaxed, thus further significantly reducing orpreventing the occurrence of cracks (delamination) at this boundary.

Fourth Preferred Embodiment

A capacitor mount series according to a fourth preferred embodiment ofthe present invention will be described below with reference to FIGS. 12and 13.

FIG. 12 is a plan view of a capacitor mount series 10 s of the fourthpreferred embodiment. FIG. 13 is a sectional view taken along lineXIII-XIII of FIG. 12.

The capacitor mount series 10 s includes a plurality of capacitors 10and a package 4. The package 4 includes an elongated carrier tape 5 anda cover tape 6. The carrier tape 5 includes a plurality of cavities 5 hspaced apart from each other and storing the plurality of capacitors 10therein. The cover tape 6 is attached to the carrier tape 5 so as tocover the plurality of cavities 5 h. The plurality of capacitors 10 arestored in the respective cavities 5 h such that the second main surfaces112 face bottom sides 5 b of the respective cavities 5 h.

The plurality of capacitors 10 included in the capacitor series 10 s areextracted from the package 4 one by one and are mounted on the mountingmember 1. More specifically, in the state in which the cover tape 6 isremoved from the carrier tape 5, by sucking and holding the capacitors10 at the side of the first main surfaces 111, the capacitors 10 areremoved from the carrier tape 5 one by one and are mounted on themounting member 1. As a result, the capacitors 10 are mounted on themounting member 1 with the second main surfaces 112 facing the mountingmember 1.

That is, by using the capacitor series 10 s of the fourth preferredembodiment, it is possible to easily manufacture the capacitor mountbody 10 x of the third preferred embodiment.

Fifth Preferred Embodiment

A manufacturing method for a capacitor according to a fifth preferredembodiment of the present invention will be described below withreference to FIGS. 14 through 16. In the fifth preferred embodiment, aprocess for forming the deformed portions 9 will be discussed in detail,which is part of the manufacturing method for the capacitor 10 of thesecond preferred embodiment.

The configuration of the boundary region of the outer portion 12 b 22with the inner portion 12 b 21 of the body 11 of the capacitor 10 isimplemented by a pressure-bonding method for a set of mother sheets.Accordingly, the pressure-bonding method for a set of mother sheets inthe fifth preferred embodiment will first be described below.

FIG. 14 is a sectional view illustrating a state in which a set ofmother sheets forming the capacitor 10 in the fifth preferred embodimentare being pressure-bonded. The set of mother sheets shown in FIG. 14 isthat as viewed from the same cross section as that shown in FIG. 9. InFIG. 14, the set of mother sheets corresponding to only two partialbodies 11 p is shown.

As shown in FIG. 14, in the fifth preferred embodiment, a plurality ofmother sheets defining the first outer layer portion 12 b 1, a pluralityof mother sheets defining the inner layer portion 11 m, and a pluralityof mother sheets defining the inner portion 12 b 21 are stacked on eachother in this order so as to provide a set of mother sheets.

A flat die 91 and a rubber 93 attached to the bottom surface of the flatdie 91 are pressed against the mother sheets defining the inner portion12 b 21 along the stacking direction, as indicated by an arrow 92 inFIG. 14, thus pressure-bonding the set of mother sheets placed on a base90.

In the set of mother sheets, the stacking density of the mother sheetsdefining the inner layer portion 11 m is higher than that of the mothersheets defining the side margin portions 12 c. Accordingly, as indicatedby the dotted lines 93 s in FIG. 14, the rubber 93 pressed against theset of mother sheets is deformed and projected downward from positionscorresponding to the inner layer portion 11 m toward positionscorresponding to the end margin portions 12 e. This causes the mothersheets at the positions corresponding to the end margin portions 12 e tobe pressure-bonded to each other and to adhere to each other.

FIG. 15 is a sectional view illustrating a state in which the set ofpressure-bonded mother sheets and a plurality of second ceramic greensheets are being pressure-bonded. In FIG. 15, the set of mother sheetscorresponding to only two partial bodies 11 q is shown. The flat die 91is pressed against the mother sheets forming the outer portion 12 b 22along the stacking direction, as indicated by the arrow 92, thuspressure-bonding the set of mother sheets and the plurality of secondceramic green sheets. As a result, a mother body is fabricated.

FIG. 16 is a sectional view illustrating a state in which the motherbody is divided. In FIG. 16, the mother body corresponding to only twopartial bodies 11 q is shown. As shown in FIG. 16, the second ceramicgreen sheets are deformed from positions corresponding to the innerlayer portion 11 m toward positions corresponding to the end marginportions 12 e in accordance with the configuration of the top surface ofthe set of pressure-bonded mother sheets, and are projected downward atthe positions corresponding to the end margin portions 12 e.

Accordingly, in the width direction W of the body 11, the boundaryregion 12 z includes deformed portions 12 zw projecting downward at thepositions corresponding to the end margin portions 12 e.

By dividing the mother body on a cut line CL, a plurality of flexiblebodies 11 q are obtained. The subsequent steps are similar to those ofthe manufacturing method discussed in the second preferred embodiment.

In the capacitor of the fifth preferred embodiment, the adherencebetween the first dielectric layers 12 x positioned in the end marginportions 12 e is enhanced. As a result, it is possible to significantlyreduce or prevent the occurrence of cracks (delamination) in the firstdielectric layers 12 x positioned in the end margin portions 12 e.

In the length direction L of the body 11, the boundary region includesdeformed portions 12 zw projecting downward at the positionscorresponding to the end margin portions 12 e. With this configuration,the outer portion 12 b 22 clamps the inner portion 12 b 21 therebetweenvia the two deformed portions 12 zw. Accordingly, a contraction forceexhibited by the thermal contraction of the outer portion 12 b 22 iseffectively applied to the inner portion 12 b 21. It is thus possible toeffectively reduce an internal stress which is produced during thefiring step due to the difference in the coefficient of thermalcontraction between the dielectric layers and the conductive layers andwhich acts on the boundary between the inner layer portion 11 m and thesecond outer layer portion 12 b 2. As a result, the occurrence of cracks(delamination) at the boundary between the inner layer portion 11 m andthe second outer layer portion 12 b 2 is significantly reduced orprevented.

A description will be given below of an experiment for examining how theheights of an inner portion and an outer portion of the body of acapacitor and the content of Si therein influence the occurrence ofcracks during a firing step and the reliability of the capacitor.

First Experiment

In a first experiment, a total of twenty-one types of capacitorsaccording to comparative examples 1 through 11 and examples 1 through 10were fabricated. Conditions (design values) applied to all thetwenty-one types of capacitors will be discussed first.

The height of the first outer layer portion is about 40 μm, the heightof the second outer layer portion is about 100 μm, the height of theinner layer portion is about 620 μm, the thickness of a conductive layeris about 0.8 μm, the number of conductive layers to be stacked is about330, and the molar ratio of Si to Ti of the first dielectric layers isabout 1.3 mol %.

The molar ratio of Si to Ti of the second dielectric layer defining theouter portion, the height of the inner portion, and the height of theouter portion of each of the twenty-one types of capacitors according tocomparative examples 1 through 11 and examples 1 through 10 areindicated in Table 1, which is shown below.

For the evaluation concerning the occurrence of cracks during the firingof the capacitors, ten samples of each of the twenty-one types ofcapacitors were prepared. If the occurrence of cracks was observed ineven one of the ten samples of each type of capacitor, the evaluationconcerning the occurrence of cracks in this type of capacitor wasdetermined to be “BAD”, and if the occurrence of cracks was observed innone of the ten samples, the evaluation concerning the occurrence ofcracks in this type of capacitor was determined to be “GOOD”. Theoccurrence of cracks was checked by exposing a WT cross section passingthrough the center of the body of a capacitor by polishing the body andby observing the exposed WT cross section with an optical microscope.

For the evaluation concerning the reliability of the capacitors, twentysamples of each of the twenty-one types of capacitors were prepared. Ifa decrease in the IR value was observed in even one of the twentysamples of each type of capacitor, the reliability of this type ofcapacitor was determined to be “BAD”, and if a decrease in the IR valuewas observed in none of the twenty samples, the reliability of this typeof capacitor was determined to be “GOOD”.

The evaluation of the reliability of the capacitors was performed byconducting a super-accelerating life test. More specifically, a voltageof about 8 V was continuously applied to each of the samples in anambient temperature of about 150° C., and then, the time taken for theIR value of each of the samples to reduce to about 10 kΩ was measured.If the time was shorter than ten hours, it was determined that the IRvalue of the capacitor was decreased.

TABLE 1 Content of Difference in Content of Si in the content of Si infirst second Si between Height of Height of dielectric dielectric firstand second inner outer layer layer dielectric layers portion portionOccurrence (mol %) (mol %) (mol %) (μm) (μm) of cracks ReliabilityExample 1 1.3 1.7 0.4 10 90 GOOD GOOD Example 2 1.3 1.7 0.4 20 80 GOODGOOD Example 3 1.3 1.7 0.4 30 70 GOOD GOOD Example 4 1.3 1.7 0.4 40 60GOOD GOOD Example 5 1.3 1.7 0.4 50 50 GOOD GOOD Comparative 1.3 1.7 0.460 40 BAD GOOD example 1 Comparative 1.3 1.7 0.4 70 30 BAD GOOD example2 Example 6 1.3 2.9 1.6 10 90 GOOD GOOD Example 7 1.3 2.9 1.6 20 80 GOODGOOD Example 8 1.3 2.9 1.6 30 70 GOOD GOOD Example 9 1.3 2.9 1.6 40 60GOOD GOOD Example 10 1.3 2.9 1.6 50 50 GOOD GOOD Comparative 1.3 2.9 1.660 40 BAD GOOD example 3 Comparative 1.3 2.9 1.6 70 30 BAD GOOD example4 Comparative 1.3 3.3 2.0 10 90 GOOD BAD example 5 Comparative 1.3 3.32.0 20 80 GOOD GOOD example 6 Comparative 1.3 3.3 2.0 30 70 GOOD GOODexample 7 Comparative 1.3 3.3 2.0 40 60 GOOD GOOD example 8 Comparative1.3 3.3 2.0 50 50 GOOD GOOD example 9 Comparative 1.3 3.3 2.0 60 40 BADGOOD example 10 Comparative 1.3 3.3 2.0 70 30 BAD GOOD example 11

Table 1 indicates the evaluation results of the first experiment. Asindicated by Table 1, in the capacitors of examples 1 through 10 andcomparative examples 5 through 9 in which the height of the outerportion was equal to or greater than the inner portion, the occurrenceof cracks during the firing of the capacitors was significantly reducedor prevented.

The reliability of only the capacitor in comparative example 5 is “BAD”.This shows that, when the molar ratio of Si to Ti of the seconddielectric layer defining the outer portion is higher than about 2.9 mol% and when the height of the inner portion is smaller than about 20 μm,the reliability of the capacitor may be decreased.

A description will be given below of an experiment for examining how theboundary region of an outer portion having a high content of Si with aninner portion of the body of a capacitor influence the occurrence ofcracks in the capacitor caused by an external stress.

Second Experiment

In a second experiment, a total of four types of capacitor mount bodiesaccording to comparative examples 12 and 13 and examples 11 and 12 werefabricated. Conditions (design values) applied to all the four types ofcapacitor mount bodies will be discussed first.

The configuration of the first outer layer is set to be similar to thatof the second outer layer portion. The height of the first outer layerportion is about 100 μm, the height of the second outer layer portion isabout 100 μm, the height of the inner layer portion is about 620 μm, thethickness of a conductive layer is about 0.8 μm, and the number ofconductive layers to be stacked is about 330.

The molar ratio of Si to Ti of the first dielectric layer and that ofthe second dielectric layer defining the outer portion and the height ofthe inner portion and that of the outer portion of each of the fourtypes of capacitor mount bodies according to comparative examples 12 and13 and examples 11 and 12 are indicated in Table 2, which is shownbelow.

For the evaluation concerning the occurrence of cracks in the capacitorsdue to an external stress, ten samples of each of the four types ofcapacitor mount bodies were prepared. If the occurrence of cracksreaching a conductive layer was observed in even one of the ten samplesof each type of capacitor mount body, the evaluation concerning theoccurrence of cracks in this type of capacitor was determined to be“BAD”, and if the occurrence of cracks reaching a conductive layer wasobserved in none of the ten samples, the evaluation concerning theoccurrence of cracks in this type of capacitor was determined to be“GOOD”.

FIG. 17 is a schematic view illustrating a state in which a substratehaving a capacitor thereon is bent in the second experiment. Theevaluation concerning the occurrence of cracks in the capacitors due toan external force was conducted in the following manner. As shown inFIG. 17, when the mounting member 1 having the capacitor 10 thereon wasbent by using a pressing tool 8, an external stress was applied to thecapacitor 10. Then, the occurrence of cracks in the capacitor 10 due tothis external force was checked.

More specifically, the occurrence of cracks in the capacitor 10 due tothis external force was checked in the following manner. In the state inwhich both ends of the bottom surface of the mounting member 1 havingthe capacitor 10 thereon were supported by two support members 7, thepressing tool 8 was vertically pressed against the top surface of themounting member 1 from upward, as indicated by an arrow 8 a in FIG. 17,so as to incline the mounting member 1 downward in a convex shape. As aresult, a tensile stress (external stress) was applied to the body 11 ofthe capacitor 10 via the two outer electrodes 14. Then, the occurrenceof cracks in the body 11 due to this tensile stress was checked. Theoccurrence of cracks was checked by exposing a cross section bypolishing the body 11 and by observing the exposed cross section with anoptical microscope.

TABLE 2 Content of Content of Si in Si in first second Height of Heightof dielectric dielectric inner outer layer layer portion portionPresence of Occurrence (mol %) (mol %) (μm) (μm) Boundary of cracksExample 11 1.3 1.7 50 50 YES GOOD Comparative 1.7 1.7 50 50 NO BADexample 12 Example 12 1.3 2.9 50 50 YES GOOD Comparative 2.9 2.9 50 50NO BAD example 13

Table 2 indicates the evaluation results of the second experiment. Asindicated by Table 2, the occurrence of cracks reaching a conductivelayer was not observed in the capacitor mount bodies according toexamples 11 and 12 in which the content ratio of Si of the outer portionwas higher than that of the inner portion. In examples 11 and 12, evenif cracks occurred in the outer portion, they did not penetrate into theinner portion. From these evaluation results, a boundary region of anouter portion having a higher content of Si with an inner portion mayhave a function of preventing cracks from reaching a conductive layer bysignificantly reducing or preventing the development of cracks orchanging the direction in which cracks develop.

Particularly, various preferred embodiments of the present invention areeffectively applicable to small capacitors in which the height of thesecond outer layer portion 12 b 2 is about 50 μm or greater, theelectrostatic capacitance is about 10 μF or higher, the length of thebody 11 is about 1.8 mm or smaller, and the number of conductive layers13 to be stacked is about 300 or greater, for example.

Among small capacitors, various preferred embodiments of the presentinvention are effectively applicable to capacitors in which the heightT₁ of the inner portion 11 m in the stacking direction of the body 11 isgreater than the width W₁ of the inner portion 11 m where a plurality ofconductive layers 13 are positioned and the height T₁ of the innerportion 11 m is greater than the width W₀ of the body 11.

Third Experiment

In a third experiment, for examining how the nonlinearity of theboundary region influences the occurrence of interface separation, seventypes of capacitors according to examples 13 through 19 were fabricated.In these capacitors, the height of the inner portion and that of theouter portion were set to be the same, and the height thereof wasvaried.

The evaluation of the nonlinearity of the boundary region was conductedin the following manner. As shown in FIG. 18, in an LT cross section ofa capacitor, a tangent line passing through a center point M of theboundary region 12 z in the length direction L and touching the boundaryregion 12 z was drawn. The shortest distance d from the intersectionbetween the end surface 113 or 114 of the body 11 and the boundaryregion 12 z to the tangent line was measured. If the shortest distance dwas smaller than about 5 μm, the nonlinearity of the boundary region 12z was determined to be “C”. If the shortest distance d was equal to orgreater than about 5 μm and was smaller than the height h₂₁ of the innerportion 12 b 21, the nonlinearity of the boundary region 12 z wasdetermined to be “B”. If the shortest distance d was equal to or greaterthan the height h₂₁ of the inner portion 12 b 21, the nonlinearity ofthe boundary region 12 z was determined to be “A”. “C” means that thenonlinearity is low and “A” means that the nonlinearity is high.

After a thermal shock cycle was applied to the fired capacitor chips byrepeatedly increasing and decreasing the temperature, LT cross sectionswere observed with an optical microscope. Ten samples of each of theseven types of capacitors according to examples 13 through 19 wereprepared. All of the ten samples of each type of capacitor were observedwith an optical microscope. If the occurrence of cracks at the interfaceof the boundary region 12 z (interface separation) was observed in evenone of the ten samples of each type of capacitor, the evaluationconcerning the interface separation in this type of capacitor wasdetermined to be “BAD”, and if the occurrence of cracks was observed innone of the ten samples, the evaluation concerning the interfaceseparation in this type of capacitor was determined to be “GOOD”. Theresults are shown in Table 3.

TABLE 3 Interface separation Height of Height of Nonlinearity after theinner portion outer portion of boundary application of (μm) (μm) regionthermal shock Example 13 20 20 A GOOD Example 14 40 40 A GOOD Example 1550 50 B GOOD Example 16 60 60 B GOOD Example 17 70 70 C BAD Example 1880 80 C BAD Example 19 90 90 C BAD

Table 3 indicates the evaluation results of the third experiment. Asindicated by Table 3, in examples 13 through 16 in which thenonlinearity is determined to be “A” or “B”, interface separation didnot occur in the capacitor chips even after a thermal shock was applied.From this result, it is seen that, in a configuration in which thenonlinearity is high, that is, the end portions of the boundary regionincline sharply, it may be possible to significantly reduce or preventthe occurrence of interface separation. Particularly, in examples 13 and14 in which the nonlinearity is determined to be “A”, not only theoccurrence of interface separation at the boundary is significantlyreduced or prevented, but also, the occurrence of cracks between theinner layer portion and the outer layer portion is significantly reducedor prevented, thus significantly contributing to reducing the structuraldefect. Table 3 shows that the nonlinearity is increased by setting theheight h₂₁ of the inner portion to be about 60 μm or smaller.

Fourth Experiment

Similarly, in a fourth experiment, for examining how the nonlinearity ofthe boundary region influences the occurrence of interface separation,seven types of capacitors according to examples 20 through 26 werefabricated. The evaluation of the nonlinearity of the boundary regionwas conducted in the following manner. In a WT cross section of acapacitor, a tangent line passing through a center point M of theboundary region 12 z in the width direction W and touching the boundaryregion 12 z was drawn. The shortest distance d from the intersectionbetween the side surface 115 or 116 of the body 11 and the boundaryregion 12 z to the tangent line was measured. If the shortest distance dwas smaller than about 5 μm, the nonlinearity of the boundary region 12z was determined to be “C”. If the shortest distance d was equal to orgreater than about 5 μm and was smaller than the height h₂₁ of the innerportion 12 b 21, the nonlinearity of the boundary region 12 z wasdetermined to be “B”. If the shortest distance d was equal to or greaterthan the height h₂₁ of the inner portion 12 b 21, the nonlinearity ofthe boundary region 12 z was determined to be “A”.

TABLE 4 Interface separation Height of Height of Nonlinearity after theinner portion outer portion of boundary application of (μm) (μm) regionthermal shock Example 20 20 20 A GOOD Example 21 40 40 A GOOD Example 2250 50 B GOOD Example 23 60 60 B GOOD Example 24 70 70 B GOOD Example 2580 80 C BAD Example 26 90 90 C BAD

Table 4 indicates the evaluation results of the fourth experiment. Asindicated by Table 4, in examples 20 through 24 in which thenonlinearity is determined to be “A” or “B”, interface separation didnot occur in the capacitor chips even after a thermal shock was applied.From this result, it is seen that, in a configuration in which thenonlinearity is high, that is, the end portions of the boundary regionincline sharply, it may be possible to significantly reduce or preventthe occurrence of interface separation. Particularly, in examples 20 and21 in which the nonlinearity is determined to be “A”, not only theoccurrence of interface separation at the boundary is significantlyreduced or prevented, but also, the occurrence of cracks between theinner layer portion and the outer layer portion is significantly reducedor prevented, thus significantly contributing to reducing the structuraldefect. Table 4 shows that the nonlinearity is increased by setting theheight h₂₁ of the inner portion to be about 70 μm or smaller.

Measurement methods for the thickness of a dielectric layer and that ofa conductive layer of a capacitor will be discussed below. FIG. 19illustrates an example of an enlarged image of a cross section of acapacitor observed with a scanning electron microscope (SEM). In FIG.19, a portion of the second main surface 112 of the capacitor in contactwith an embedding resin 29 is shown.

When measuring the thickness of a dielectric layer and that of aconductive layer of a capacitor, the following method is used. In anenlarged image of a cross section of a capacitor observed with a SEM, asshown in FIG. 19, a straight line Lc extending in the stacking directionof the body of the capacitor and passing through the center of the bodyis drawn. Then, a plurality of straight lines parallel with the straightline Lc are drawn at equal pitches S. The pitch S may be set to be aboutfive to ten times as long as the thickness of a dielectric layer or thatof a conductive layer to be measured. If, for example, a dielectriclayer having a thickness of about 1 μm is measured, the pitch S is setto be about 5 μm. The number of lines drawn on one side and that on theother side of the straight line Lc are the same. That is, an odd numberof lines including the straight line Lc are drawn. In FIG. 19, anexample in which five straight lines La through Le are drawn is shown.

Then, on each of the lines La through Le, the thickness of a dielectriclayer and that of a conductive layer are measured. If, on each of thestraight lines La through Le, a conductive layer is missing anddielectric layers join each other with the conductive layertherebetween, or if an enlarged image at a portion to be measured is notclear, the thickness or the distance is measured on another straightline separated from the straight line Lc.

When measuring the thickness of a dielectric layer 12, as shown in FIG.19, the thickness D₁ on the straight line La, the thickness D₂ on thestraight line Lb, the thickness D₃ on the straight line Lc, thethickness D₄ on the straight line Ld, and the thickness D₅ on thestraight line Le are measured, and the average value thereof is set tobe the thickness of the dielectric layer 12.

When calculating the average thickness of the plurality of dielectriclayers 12 included in the inner layer portion 11 m, the thicknesses of atotal of five dielectric layers 12 constituted by the dielectric layer12 positioned substantially at the center of the inner layer portion 11m in the thickness direction T and two dielectric layers 12 positionedat each of both sides of this dielectric layer 12 are measured by usingthe above-described method, and the average value thereof is set to bethe average thickness of the plurality of dielectric layers 12 includedin the inner layer portion 11 m.

If the number of stacked dielectric layers 12 is less than five, thethicknesses of all the dielectric layers 12 are measured by using theabove-described method, and the average value thereof is set to be theaverage thickness of the dielectric layers 12.

A method for measuring the width of the side portion margins 12 c is asfollows. A WT cross section passing through the center of the body 11 isexposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the side margin portion 12 c having the largest widthis measured.

A method for measuring the length of the end portion margins 12 e is asfollows. An LT cross section passing through the center of the body 11is exposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the end margin portion 12 c having the largest lengthis measured.

A method for measuring the width W₁ of the inner layer portion 11 m isas follows. A WT cross section passing through the center of the body 11is exposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the widths of the first outermost conductive layer 13,the second outermost conductive layer 13, and the conductive layer 13positioned closest to the center of the inner layer portion 11 m in thestacking direction are measured, and the average value of the threemeasured widths is calculated.

A method for measuring the length L₁ of the inner layer portion 11 m isas follows. An LT cross section passing through the center of the body11 is exposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the lengths of the first outermost conductive layer13, the second outermost conductive layer 13, and the conductive layer13 positioned closest to the center of the inner layer portion 11 m inthe stacking direction are measured, and the average value of the threemeasured lengths is calculated.

A method for measuring the height T₁ of the inner layer portion 11 m isas follows. A WT cross section passing through the center of the body 11is exposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the length of a line segment passing through thecenter of the body 11 and connecting the first and second outermostconductive layers 13 with the shortest distance is measured.

A method for measuring the height h₁ of the first outer layer portion 12b 1 or the height h₂ of the second outer layer portion 12 b 2 is asfollows. A WT cross section passing through the center of the body 11 isexposed by polishing the body 11 and is observed with an opticalmicroscope. Then, the height h₁ of the first outer layer portion 12 b 1or the height h₂ of the second outer layer portion 12 b 2 at the centerof the body 11 in the width direction W is measured.

Analysis for the composition of components contained in the firstdielectric layer 12 x or the second dielectric layer 12 y may beconducted by using inductively coupled plasma (ICP) emissionspectrometry or a WDX. If elemental analysis is conducted by using ICPemission spectrometry, a sample is formed into a powder and is dissolvedwith an acid. Then, the resulting solution is subjected to ICP emissionspectrometry, thus specifying the composition. If elemental analysis isconducted by using a WDX, a WT cross section is exposed by polishing thebody of a capacitor embedded in a resin, and then, the composition isspecified by using a WDX attached to a SEM.

The boundary region of the outer portion having a high content of Siwith the inner portion may be identified as follows. A WT cross sectionis exposed by polishing the body of a capacitor embedded in a resin, anda backscattered electron image of the exposed WT cross section iscaptured and observed by using a SEM. Alternatively, the boundary regionmay be identified by creating element mapping of the exposed WT crosssection by using a WDX attached to a SEM and by specifying a portionhaving a high content of Si.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: a bodythat includes a plurality of dielectric layers and a plurality ofconductive layers stacked on each other in a stacking direction and thatincludes first and second main surfaces opposing each other in thestacking direction, first and second end surfaces opposing each other ina length direction and connecting the first and second main surfaces,and first and second side surfaces opposing each other in a widthdirection and connecting the first and second main surfaces and thefirst and second end surfaces; and first and second outer electrodesthat are disposed on portions of a surface of the body; wherein theplurality of conductive layers include first conductive layers connectedto the first outer electrode and second conductive layers connected tothe second outer electrode; the body includes a first outer layerportion including a first of the plurality of dielectric layers definingthe first main surface, a second outer layer portion including a secondof the plurality of dielectric layers defining the second main surface,and an inner layer portion adjacent to both of the first outer layerportion and the second outer layer portion, the inner layer portionincludes a portion extending from a first outermost conductive layerpositioned closest to the first main surface among the plurality ofconductive layers through a second outermost conductive layer positionedclosest to the second main surface among the plurality of conductivelayers; the second outer layer portion includes an outer portionincluding the second main surface and an inner portion disposed adjacentto both of the outer portion and the inner layer portion; a height ofthe inner layer portion in the stacking direction is larger than a widthof the body in the width direction; a composition ratio of Si relativeto Ti of the outer portion is higher than that of the inner portion; andthe second outer layer portion is thicker than the first outer layerportion.
 2. The multilayer ceramic capacitor according to claim 1,wherein the outer portion includes a boundary region adjacent to theinner portion, the boundary region has a larger Si content than acentral region of the outer portion in the stacking direction.
 3. Themultilayer ceramic capacitor according to claim 1, wherein the bodyincludes side margin portions between the inner layer portion and thefirst and second side surfaces in the width direction; and an averagewidth of the side margin portions is greater than a height of the firstouter layer portion in the stacking direction.
 4. The multilayer ceramiccapacitor according to claim 1, wherein the body includes side marginportions between the inner layer portion and the first and second sidesurfaces in the width direction; and an average width of the side marginportions is greater than about 30 um and less than about 90 um.
 5. Themultilayer ceramic capacitor according to claim 1, wherein the outerportion includes a boundary region adjacent to the inner portion; and asviewed from the width direction, the boundary region includes a portionwhich inclines toward the first main surface as the boundary region getscloser to one of the first and second end surfaces.
 6. A multilayerceramic capacitor comprising: a body that includes a plurality ofdielectric layers and a plurality of conductive layers stacked on eachother in a stacking direction and that includes first and second mainsurfaces opposing each other in the stacking direction, first and secondend surfaces opposing each other in a length direction and connectingthe first and second main surfaces, and first and second side surfacesopposing each other in a width direction and connecting the first andsecond main surfaces and the first and second end surfaces; and firstand second outer electrodes that are disposed on portions of a surfaceof the body; wherein the plurality of conductive layers include firstconductive layers connected to the first outer electrode and secondconductive layers connected to the second outer electrode; the bodyincludes a first outer layer portion including a first of the pluralityof dielectric layers defining the first main surface, a second outerlayer portion including a second of the plurality of dielectric layersdefining the second main surface, and an inner layer portion adjacent toboth of the first outer layer portion and the second outer layerportion, the inner layer portion includes a portion extending from afirst outermost conductive layer positioned closest to the first mainsurface among the plurality of conductive layers through a secondoutermost conductive layer positioned closest to the second main surfaceamong the plurality of conductive layers; the second outer layer portionincludes an outer portion including the second main surface and an innerportion disposed adjacent to both of the outer portion and the innerlayer portion; a height of the inner layer portion in the stackingdirection is larger than a width of the inner layer portion in the widthdirection; a composition ratio of Si relative to Ti of the outer portionis higher than that of the inner portion; and the second outer layerportion is thicker than the first outer layer portion.
 7. The multilayerceramic capacitor according to claim 6, wherein the outer portionincludes a boundary region adjacent to the inner portion, the boundaryregion has a larger Si content than a central region of the outerportion in the stacking direction.
 8. The multilayer ceramic capacitoraccording to claim 6, wherein the body includes side margin portionsbetween the inner layer portion and the first and second side surfacesin the width direction; and an average width of the side margin portionsis greater than a height of the first outer layer portion in thestacking direction.
 9. The multilayer ceramic capacitor according toclaim 6, wherein the body includes side margin portions between theinner layer portion and the first and second side surfaces in the widthdirection; and an average width of the side margin portions is greaterthan about 30 um and less than about 90 um.
 10. The multilayer ceramiccapacitor according to claim 6, wherein the outer portion includes aboundary region adjacent to the inner portion; and as viewed from thewidth direction, the boundary region includes a portion which inclinestoward the first main surface as the boundary region gets closer to oneof the first and second end surfaces.